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How do you measure the brightness of a polished metal surface? - Doug Ayen's Blacksmithing Blog [entries|archive|friends|userinfo]
Doug Ayen

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How do you measure the brightness of a polished metal surface? [Jan. 24th, 2015|04:29 pm]
Doug Ayen
How do you measure the brightness of a polished metal surface?

During a recent knifemaker symposium, the topic of stainless damascus came up with the stated problem that nobody really knows which high carbon stainless steels (HCSS) have the greatest contrast. In fact, the expert said in his opinion it was just easier to mix in either non-stainless (D2, L6) or non-high-carbon stainless (305, 315, 420, etc) and accept the inconsistency in the final product. What I would like to do is take a sample of each common HCSS (ats34, bg42, 440c, sv30v, etc), say 20mmx20mm, heat treat, polish to a standard grit, probably .5 micron(A5, 1500 grit ANSI) and then measure the brightness, or reflectivity of the surface, then etch with some standard etchants and see what that shows.  The problem is, I'm not sure what to use to do the measurement. Back when I did typesetting, we used a reflectance densitometer to do something similar, but I'm not finding the right tool. Any suggestions?

Ideally, what I'd want is a calibrated light source aimed to reflect off the surface at a specific angle and hit a photoreceiver that can measure how much of that light is being received. The comparative numbers should give a better idea of what existing HCSS would have the highest contrasts, and given the metalurgical analysis of the respective steels, might suggest alloy formulations to try for an even higher contrast. Just don't know what the tool would be to do that measurement.
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